Building a home in space

The drawing was simple, almost crude, but direct. And it would change space history.

On Aug. 19, 1966, George Mueller, NASA associate administrator for Manned Space Flight, sketched an idea for a simple space station built from a spent Saturn S-IVB stage designed for the Apollo moon landing program.

Muller had sketched the first blueprint for what would become Skylab, launched 40 years ago, May 14, 1973.

The basic idea was not new. For years space engineers had envisioned converting expended rocket tanks into space stations. After all, the two items contain a pressurized fluid, either rocket fuel or crew air.

Wernher von Braun, the German rocket engineer who would later direct NASA's Marshall Space Flight Center in Huntsville, Ala., in the late 1950s had outlined Project Horizon, a then-classified U.S. Army concept for a large manned moon base. In 1958, Krafft Ehricke at General Dynamics designed Outpost, an Atlas ballistic missile converted in orbit into a space station. In either case the rocket stage was just 10 feet wide, making for cozy accommodations.

Earth-orbit space stations lost priority on May 25, 1961, when President Kennedy challenged the nation to put a man on the moon "before this decade is out." That refocused everyone's efforts and, ironically, improved options for a space station.

Going to the moon required an immense rocket.

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What evolved was the Saturn V, with first and second stages set at 33 feet in diameter, and the third stage at nearly 22 feet. Even while all hands turned to designing and building the massive rocket, many at NASA were considering other missions for Apollo hardware, including the third stage. Douglas Aircraft, builder of the third stage, had been pushing such an idea for some time. And the Soviet Union used a similar approach in its Salyut series of space stations starting in late 1971.

What started as the Apollo Extension System soon became the Apollo Applications Program, or AAP. The Huntsville team envisioned a "wet workshop," using the smaller Saturn IB rocket to orbit its second stage, virtually identical to the Saturn V's S-IVB third stage, with a docking adapter and other gear attached. An astronaut crew would be launched next to outfit the stage's roomy liquid hydrogen tank almost 22 feet wide as an orbital workshop. Later flights would add a Lunar Module outfitted with an array of telescopes to study the sun.

But problems with early spacewalks on the Gemini missions showed that working in space was more challenging than expected. What if the astronauts couldn't get things assembled and working? Some engineers started promoting the idea of a "dry workshop" that would be assembled on the ground and open for business hours after arriving in space.

The turning point came in 1969 when Mueller discovered a bit of bootleg engineering. Von Braun and his team had built an immense swimming pool, 80 feet wide and 40 feet deep, where spacecraft mockups could be submerged for space-suited engineers to test spacewalk procedures. Despite not being formally approved, Mueller liked it and took a turn.

He came out realizing that outfitting the wet workshop was impractical.

"Once I tried even the simple task of closing the valves between the tanks," Mueller recalled in Homesteading Space: The Skylab Story, "it convinced me that we wouldn't rebuild and refurbish the tank in orbit, so that led me to the decision to go with the dry workshop."

It would be a turn-key operation: Launch the "dry workshop" the fully converted S-IVB and the Apollo Telescope Mount with solar telescopes atop a two-stage Saturn V, activate remotely, launch the crew the next week on a Saturn IB, and go to work in what was now called Skylab.

But to paraphrase Rick in Casablanca, "It seems that destiny has taken a hand." A major mishaps that almost destroyed the station forced NASA to contrive repairs that involved spacewalks more complex and daring than what they had tried to avoid by switching to the dry workshop.

Skylab's original design included a micrometeoroid shield that would expand outward by a few inches from the pressure vessel. It was retained as the solar shield even after new data showed that the micrometeoroid hazard was not as great as once feared.

But Skylab engineers made a crucial error. The stowed shield was not attached tightly to the stage, and 63 seconds after liftoff, aerodynamic effects ripped the shield from the workshop, and damaged a solar array enough that it later pulled away. Some of the debris struck the interstage, the cylinder joining first and second stages. Film of this cleanly falling away in the first Saturn V launch, Apollo 4, is one of the most-used space movie clips. On this last flight, the damage from the falling shield held it in place.

Now came one of the weirdest coincidences in space history. The interstage was a massive structure, weighing almost five tons. Lugging that along would have placed Skylab in a lower orbit than planned, perhaps too low to be safely manned.

But the interstage also increased the thrust of the second stage just enough to make up the difference. Even though a rocket's exhaust is directed downward, in the upper reaches of the atmosphere a small amount will recirculate around the base of the rocket. On Skylab, the stuck interstage acted like a large nozzle extension, trapping some of that recirculating exhaust so it pushed upward instead of outward in all directions.

Skylab safely reached orbit and NASA soon was grappling with how to repair it in orbit. In the end, NASA managers would declare that Skylab was more successful broken than if everything had worked as planned because they were able to demonstrate the utility to humans in space.